Vinification of unripe red grapes: Impact of partial seed removal, ultrasound and stems on wine quality

Harvesting and vinifying less mature grapes can help reduce high alcohol levels in wines, a growing issue related to the imbalance between technological and phenolic maturity due to climate change. However, unripe grapes contain poorly lignified seeds and show lower extraction of skin phenolics, negatively affecting sensory quality. This study evaluated partial seed removal (EP) combined with techniques to enhance skin compound extraction, such as ultrasound (EP US), or to compensate for lower tannins through controlled stem addition (25% or 50%) in ‘Monastrell’ wines from unripe grapes. Physicochemical, phenolic, colour and aromatic parameters and sensory attributes were evaluated. Partial seed removal decreased tannin content and astringency, improving mouthfeel. Ultrasound increased skin tannin extraction and stable pigment formation. Adding 25% stems raised tannin levels and fruity esters, whereas 50% stems produced herbaceous notes. Overall, combining seed removal with physical techniques and moderate stem inclusion improved colour and sensory balance in lower-alcohol wines.